1. Field of the Invention
This invention relates exclusively to a species of pump, sometimes operable as a motor, known as a slipper vane pump. More specifically, the present invention relates to a specific construction of a slipper vane pump of the expanding chamber type wherein the tangent arc or crossover point is sealed by interposing a minimum of one slipper pumping vane in the tangent arc sealing position at all times.
2. The Prior Art
The slipper vane pump art is represented by such prior art as patents of William H. Livermore, Hubert M. Clark and Gilbert H. Drutchas. Typical is U.S. Pat. No. 3,200,752. Most of such prior art is centered on a form known to persons skilled in the art as a tangent arc seal. Such pump-type characteristically provides a rotor diameter seal at the crossover point between the outlet and inlet ports of a typical expanding chamber-type pumping unit.
The general concept of a so-called sllipper seal design wherein a minimum of one slipper is interposed into a tangent arc sealing position at all times has been described in the prior art. However, none of the pump constructions heretofore disclosed in the prior art are capable of meeting the noise and high speed durability characteristics vital to achieving the current order of sophistication required for high pressure hydraulic power applications, for example, for use as power steering pumps on dirigible vehicles. Due to the complexity of the noise-generating phenomena and the dynamic perturbations resulting from the virtual free-body action of the slipper pumping vane, concise positioning and specific geometric proportions are absolutely essential in order to achieve a pump which is satisfactory for widespread commercial usage and in order to achieve a status of commercial acceptability.
Those familiar with slipper pump art will appreciate the problems associated with achieving a quiet high tangent arc clearance pump design for automotive use, for example. Typically, since 1955, the designs of slipper pumps for power steering have not included a slipper seal design since no commercially quiet slipper pumps have existed. Early commercial slipper transmission pumps utilized the slipper seal approach, however, these pumps were of the round-bore type and operated up to a maximum pressure level of 250 psi, as contrasted with the performance specifications of contemporary power steering pump applications which may require delivered pump pressure of 1500 psi or greater. Ultimately, such prior art designs became obsolete due to the high level of noise.
In the pump construction exemplified by U.S. Pat. No. 3,200,752, which pump was produced in large quantities and used extensively in the automobile industry as a power steering pump, such pump did not require these parameters to maintain a commercial noise level since its clearance volume was limited by virture of being a tangent arc pump. However, heat rise, due to rotor rub, remains a characteristic problem to the artisan working in this field. Early experimenters in slipper seal art attempted to avoid such problems by maintaining a close tangent arc clearance. This has led to continuation of the current production problem syndrome of close rotor hit problems with high system heat rise due to rotor-cam rubbing attrition.
It will also be appreciated by those experienced in the slipper pump art that the configurations applicable to the conventional vane design or the vane roller are set apart from the needs of the slipper pumps. The former maintains a close fit vane-to-slot as low as 0.0002 nominally, virtually restricting any perceptible fore and aft motion in the rotor slot, while the roller vane utilizes a contoured slot that constrains the roller position fore and aft in the slot to a workable maximum.
On the other hand, the slipper pumping vane, a substantially rectangular body, is accelerated forward in the slot clearance by the action of high pressure outlet fluid and the decreased pressure state on the fore of the slipper as the rotor turns through the tangent arc from outlet to inlet. If not controlled, the slipper pumping vane rapidly checks to the front rotor slot which presents a high pressure level to its rearward trailing trapped annulus. Large or excessive clearance thus results in comparatively large pressurized oil pressure parcels entering the inlet port through the clearance volume causing virtual explosive turbulence in the inlet. The turbulent eddys produce an outward token noise, and, in turn, act to prevent the proper fill under the slipper traversing through the inlet port.
It appears from our studies that the slipper action with low centrifugal force and the lack of solid oil is not conducive to forcing the slipper to reseat against its driving edge. Failure to do so, prevents the slipper from effecting a proper seal in the working arc, thus, causing a flow pulse and a perceptible pressure peaking at the point of inlet port closure, since some high pressure oil can escape to the inlet and thus add another source of noise to the pump. Since the relative time span of each of the dynamic actions of the slipper pumping vane are finitely minimal time frames, it is difficult to provide control means that do not under or over compensate the slipper pumping vane action.